1. Field of the Invention
The present invention relates to a sheet for forming process and a method for manufacturing the same, an image forming method, a method for manufacturing a forming processed product and the resulting forming processed product, and particularly to a sheet for forming process used suitably for manufacturing a three-dimensional article and the method for manufacturing the same, an image forming method, a method for manufacturing a forming processed product and the resulting forming processed product.
2. Description of the Related Art
Recently, a means for forming images of the same quality massively and inexpensively by a variety of printing methods such as hand gravure process, relief process, planography, gravure printing, and screen printing is known with developments of image forming technology. Such printing methods are widely used for face printing of image displaying articles (wallpapers, advertisement boards, clock boards, industrial goods such as switches, and dummy cans for automatic dispensers).
However, in the screen printing, for example, a number of printing plates corresponding to the number of images to be printed is required. In case color printing, the number of printing plates corresponding to those to be required for printing is necessary, resulting in a rather expensive cost. In some cases, printing plates once prepared are washed and stored, so that a wide space must be assured for the storage. Besides, even when there is a minor change in design, it is required that fresh printing plates are prepared and the previous matrices are replaced by the fresh ones. Therefore, such printing method as described above is unsuitable for limited production of a wide variety of goods.
On the contrary, an image formation (printing) according to an electrophotographic method is carried out by such a manner that a surface of an image carrying member is uniformly charged, exposed in response to image signals to form an electrostatic latent image due to a potential difference between exposed regions and unexposed regions, thereafter, color powders (image forming materials) called by the name of toners having a polarity reverse to (or the same as) that of the above-described charge are developed electrostatically, whereby a visual image (toner image) is formed on the surface of the image carrying member. In case of a color image, the color image is obtained by such a manner that either the above-described step is repeated plural times or a plurality of image forming devices are parallely arranged to form visual images, and these images are transferred to an image recording body, and fixed thereon (immobilization: solidification by melting and cooling color powders by means of essentially heat).
As mentioned above, according to an electrophotographic method, as long as there is electronic data, not only the same image can be formed repeatedly, but also it can easily be responded to a design modification or a different image, and such an image can be formed accordingly. Moreover, a toner image on the surface of an image carrying member can be substantially completely transferred to a surface of an image recording body, and even if the toner image remained slightly on the surface of the image carrying member, it can be easily removed by a resin blade, a brush and the like. Accordingly, printed materials can be easily prepared for limited production of a wide variety of goods.
The above-described toner is prepared usually by melt-mixing a hot-melt resin, a pigment, and an additive such as a charge control agent according to circumstances, and grinding and pulverizing the resulting melt-mixed product. A latent image in the electrophotographic method exhibits considerably high resolution as compared with the pulverized toner, and sufficient resolution can be expected in comparison with that of the screen printing, or that of an ink ribbon in a thermal transfer system.
With respect to a color image, four primary colors of cyan, magenta, yellow, and black are used in color toners, and when these toners are mixed, colors can be theoretically reproduced as in the case of printing. Besides, a toner resin can be incorporated comparatively freely with pigments in the toners, so that an image masking property by the toners can be increased easily.
The base material (core) which is most frequently used for a variety of dummy cans or the like at present is a polycarbonate sheet. The reason of which is in that polycarbonate sheet is excellent in printing characteristics and also in forming process suitability (convexoconcave processing). However, when such polycarbonate sheet applied to electrophotography without any modification, a toner being an image forming material cannot be sufficiently transferred thereto, and it results in poor image quality, because the sheet surface of polycarbonate is insulative.
Since a polycarbonate sheet is an insulative material, static electricity generates easily, so that there is a case where it scatters a toner image to deteriorate its image quality, or a case where it adsorbs dust. Besides, since a friction coefficient between sheets is too high, there is such a problem that sheets stick with each other, and it results in poor sheet conveyorability. As a result, sheets are conveyed in an overlapped state in an electronograph.
When it is intended in an electronograph to print out images on a resin sheet as used in forming process which softens comparatively at a low temperature, a surface tack appears in a fixing step, because a fixing temperature is higher than a softening temperature of a film, and thus, there is a problem of occurrence of enwinding jam in a fixing device. In addition, there is a case where image forming materials are offset in the fixing device.
Hence, it brings about troubles of a transfer of such image forming materials to a film surface, so that the equal resolution to that of thermal transfer system cannot be obtained.
An example of a plastic sheet which has been heretofore used for sheet forming technique includes rigid or flexible polyvinyl chloride (PVC) sheets, polypropylene (PP) sheets, polystyrene (PS) sheets, ABS sheets, and polycarbonate (PC) sheets.
Among others, an inexpensive rigid PVC sheet having excellent transparency has been generalized, however, an amorphous polyethylene terephthalate (A-PET) sheet which does not contain any chlorine atom, thus it is excellent in non-toxicity, transparency, and surface gross, has been recently watched as a thermoformable sheet. Such highly transparent A-PET sheet is obtained by cooling quickly and forcibly polyethylene terephthalate to be an amorphous state by means of cooling rolls at the time of extruding a sheet. The A-PET sheet is excellent in thermoforming and transparent, so that a fair container can be formed. However, crystallization begins to proceed at a sheet temperature of from around 100° C. onward in case of formation, at the same time; there is a defect of whitening.